Ladybirds used for biological pest control which may be
accidentally imported to Britain
Paul Mabbott 49 Endowood Road Sheffield S7 2LYpaulmabbott@blueyonder.co.uk
There is a commendable tendency world-wide towards encouraging natural predators
of crop pests rather than applying pesticides. Ladybirds, as avid consumers of homopteran
pests (aphids, whitefly, scale insects etc), are widely employed. Given the vast amounts
of food imported into this country, especially 'organic' produce, some of these insects
are likely to turn up in our shopping from time to time. Imported ornamental plants and
trees are another source of exotic fauna.
Biological control may be achieved in many ways. For instance, by providing conditions
to encourage population growth of local species; by culturing native species to augment
local populations; or by importing foreign species to counter pests which have no native
predators. The latter needs careful consideration: imported species may switch prey and
become competitors of local species. Large numbers of exotic species have been imported
to America sometimes to the detriment of the local fauna. At least two species of imported
ladybird seem to have had harmful effects in America: our European 7-spot (Coccinella
septempunctata) has become the most common ladybird in NE USA and Canada with
apparent declines in many indigenous species.
Imports to Britain have been more stringently controlled and only one species,
Cryptolaemus montrouzieri (Plate 6), confined to greenhouse crops, has been sanctioned.
Species designed for glasshouse control are assumed to be safe since escapees would be
unable to tolerate British winters. Despite this C. montrouzieri was noted to persist
sporadically outdoors at Wisley. Imports into this country are most likely to be accidental:
Neil Harvey and myself noted the import of the South African species Cheilomenes
lunata during 2002. In the same year a single specimen of the South American species
Eriopsis connexa was found in a supermarket in Harrow.
Last year a specimen of the Vedalia beetle (Rhodolia cardinalis ) was found in a Chelsea
garden. What is perhaps so amazing about this discovery is that it has taken so long for
the animal to arrive: R. cardinalis was the first insect to be successfully employed in
pest control when it was established in California in 1889 to control the cottony-cushion
citrus scale, Icerya purchasi. The Australian beetle has subsequently been exported
throughout the warmer parts of the world (the specimen in Plate 7 was photographed in
Avignon). It has not become a pest and seems not to compete harmfully with native
species. Such casual imports from sunnier climes are unlikely to be problematic until
the climate becomes considerably warmer.
A greater threat is posed by invaders from similar weather and vegetation zones. There
are numerous species in continental Europe not found on the British Isles, perhaps these
12
Essex Field Club Newsletter No. 44, May 2004